1. Field of the Invention
The present invention relates generally to structures for supporting the human body while seated, and, in particular, to an improved cushioned sling seat structure which is designed to optimize the comfort and stability of the user.
2. Description of the Prior Art
There has been much research conducted over the years to attempt to improve the comfort of structures which serve to support the human body in a sitting position. It is well known that individuals who are required to sit for long periods are subject to discomfort, fatigue, pain, and various other afflictions associated with the lack of proper support of the torso of a person seated in an erect position over a sustained period of time. A common example of this problem occurs with individuals confined to wheelchairs. The lack of movement in this sitting position restricts blood flow, causing mechanical damage to body tissues and often leads to painful sores and ulcers.
Many attempts have been made to alleviate, if not prevent, these problems. These developments generally fall into several categories.
The most common types of cushions which have been used to address these problems are foam cushions. Foam cushions are popular, as they are lightweight, fairly durable, and inexpensive to manufacture. Foam pads with cut-out areas, convoluted surfaces, wedge-shaped slots and cored-out sections have been developed to minimize the adverse effects on the human body. Examples of these devices are taught in U.S. Pat. Nos. 4,042,987; 4,713,854; 3,111,689; 2,047,616; 3,337,884; and 3,222,694. There are several disadvantages, however, to the use of foams in cushions; foam generally has poor shear and tension properties, and also suffers from the inability to distribute loads or restoring forces evenly.
Another type of cushion which has been tried is a gel cushion. This type of cushion uses a viscous substance contained within some type of flexible structure capable of conforming with the body contours in contact with the cushion. While these cushions possess favorable tension and shear/friction properties, they are often heavy and bulky, and tend to deteriorate with heavy use. Examples of these cushions are taught in U.S. Pat. Nos. 3,858,379; 3,308,491; 3,663,973; 3,689,948; 4,728,551; 4,726,624; 5,336,708; 5,334,646; and 4,588,229.
Still another type of cushion which has been tried is a fluid-filled cushion. this type of cushion uses a fluid, such as gas or liquid, contained within a flexible envelope to allow the envelope to conform to the body contour. While gas-filled cushions are very light and inexpensive, the buoyancy is zero and the support of the body depends on a suitable hammock effect of the envelope plus the pressure of the air inside. Stability is generally greater with air filled cushions than that of liquid filled cushions because of increased tension in the envelope. Examples of the fluid filled cushions are shown in U.S. Pat. Nos. 2,823,394; 3,251,075; and 3,984,886.
Another type of cushion design which is available in the markeplace is the thixotropic, or xe2x80x9cputty-filledxe2x80x9d cushion. These cushions generally conform to the body in a suitable fashion as the material flows, can stiffen under fast loading to provide a solid and comfortable base for the body, and are designed to accurately control the flow of the material inside the cushion. However, this type of cushion tends to be fairly heavy, making it somewhat awkward to handle, can bottom out in some instances and tend to be relatively expensive compared to other cushions available. Examples of these cushions are taught in U.S. Pat. Nos. 4,726,624; 4,588,229; 4,728,551; and 5,018,790.
Finally, some cushion designs attempt to combine different features from the cushion types previously discussed to attempt to improve upon its performance. U.S. Pat. No. 2,819,712 combines a foam cushion with an air filled bladder; U.S. Pat. No. 5,524,971 uses a combination of fluid layers combined with foam layers; and U.S. Pat. No. 5,513,899 uses an envelope filled with a combination of petrolatum and hollow glass spheres.
While there have been many attempts to provide a superior cushion to satisfy a diverse range of users, each design has particular deficiencies which make it difficult to gain universal acceptance. The one feature which is present in all of the aforementioned cushions is the fact that they all are subject to compression forces.
It is therefore an object of the present invention to provide a cushion which will provide maximum contact surface area along with uniform pressure on the body by spreading the forces away from high pressure areas using multiaxis tension forces.
It is also an object of the present invention to provide a seat which is inexpensive, lightweight, and durable, and offers stability.
It is a further object of the present invention to provide a cushion which can provide comfort and ventilation for a person seated for long periods of time without causing injury or fatigue.
These and other objects are accomplished in the present instance by a sling seat consisting of a thin and flexible material having non-uniform properties which allows the material in tension to adapt to the contour of the rear of the person seated. A person cannot sink into a compression type cushion more than the thickness of the cushion. In this tension type design, the ischial tuberosities of a person seated in the cushion are suspended, and will not xe2x80x9cbottom outxe2x80x9d in the cushion. By controlling the pressures on the ischial tuberosities and the coccyx of persons seated on a cushion manufactured according to the present invention, physical problems such as ulcers can be avoided in persons who must sit for long periods of time. Different embodiments of the invention are taught having features which enhance the desirable properties of the sling seat.